Hi,

So the most important question is, which question types I should put my 15 videos in to get what I want? 

I do not see ypour problem. If there is one correct answer and out of the five options, of course you should use a list(radio).

I would like to see the total time spent, and correct amount of answers from and on those 15 questions

Who would like to see? You or the respondent?
If you want to show this to the respondent you have to measure the time by two equations, that only contain the function {time()}
So you will get two UNIX timestamps and the difference is the used time in seconds.
And the amount of correct answers you calculate again by an equation, like {sum(if(Q1==1,1,0),if(Q2==2,1,0),if(Q3=,1,0),if(Q4==1,1,0))}
Assuming that the correct answers were
1 in Q1
2 in Q2
3 in Q3
1 in Q4

Well, now you should create a full survey (no need to include 20 videos, only placeholder questions like "This is video 1", "This is video 2", ...).
As I said before, the video questions are randomized by entering the same "randomization group name" into all these questions.

Joffm

And there is a workaround to display side by side.
Here an example
 

I wouldn't recommend in this case.
Better use "bootstrap buttons" for your answers (well, depends on the length of the texts)